Radio telephone system



is uti-bmw@ SEARCH ROOT Aug. 19, 1952 F. E. GlssLER Erm. 2,507,837

" I RADIO TELEPHONE SYSTEM Filed April 22, 1950 4 Sheets-Sheet l F. E. GISSLER ETAL RADIO TELEPHONE SYSTEM` Aug. 19, 1952 4 Sheets-Sheet 2 Filed April 22, 1950 EEG/SSLER /N VEN TORS AT TOR/ver l Aug. 19, 1952 l F. E. GlssLER ET AL. 2,607,887-

RADIO TELEPHONE SYSTEM Filed April 22, 195o 4 sheets-sheet s H" wml-H FIG 4 CONTROL UNIT saw" AAA

lz" EG/SSLER /NVENro/Qs. J FLA/DIG ATTORNEY Aug. 19, 1952 F. E. GlssLER ErAL 2,607,887

RADIO TELEPHONE SYSTEM Filed April 22. 1950 4 Sheets-Sheet 4 N l' nl-... I-III N l T g J I E 8 m l` 't n B' Q' D F E. G/SSLER /NVE/vrons J ELA/0,6

ATZ'ORNEV Patented Aug. 19, 1952 RADIO TELEPHONE SYSTEM Frank E. Gissler, Denville, and John F. Laidig,

Mine Hill Township, Morris County, N. J., assignors to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application April 22, 1950, Serial N0. 157,598

(Cl. Z50-6) 23 Claims.

`This invention relates to radio telephone communication systems and, more particularly, to a radio telephone system having an unattended coin box controlled radio telephone station located on a. passenger vehicle which, throughout this specification, will be referred to as a railroad train but is not limited to this particular type of vehicle.

Since the route of the railroad train passes through certain geographic areas having no radio telephone facilities and in which radio telephone service is not available, it is desirable that the radio telephone station on the train be equipped with a readily discernible indicator which will be actuated only when the train is traveling through a zone in which radio telephone service is available. As the portion of the frequency spectrum that is assigned as a, communication channel for use by the radio station on the train is also assigned for use by other radio stations, it is also desirable that the telephone service available indicator on the train be automatically controlled so that it will not be operated when the communication channel is being used by another radio station. ;Since there is no supervisory attendant at the radio station on the train, it is necessary to further control automatically the @telephone service available" indicator on the train so that it will not be operated when the instantaneous signal-to-noise ratio is not satisfactory for commercial use of the system by a passenger on the train. In addition, it is necessary that an operator at a radio terminal station be able to discontinue the operation of the radio transmitter on the train by remote control after it has inadvertently been left in operation due to failure to restore the train telephone instrument -to its holder.

Accordingly, it is an object of this invention to provide a radio telephone mobile station with an indicator which will be operated automatically when the station moves into a zone having radio telephone facilities.

It is also an object of the invention to automatically restrict the operation of the indicator to periods when the radio telephone system is not busy.

A further object is to automatically limit the operation of the indicator to periods when the existing signal-to-noise ratio-is satisfactory for communication purposes.

An additional object is to discontinue the operation of the radio transmitter on the train by remote control after it has inadvertently been left in. operation due-to failure to restore the train telephone instrument to its holder.

These and other objects of the invention are attained in a manner now to be described briefly which includes providing a radio terminal station with a low frequency tone for modulating the carrier during idle periods. When the radio station on the train is within range of the terminal station, the tone modulated carrier is received. The low frequency tone is separated by filtering and is employed to effect the energization of a relay which controls the operation of a telephone service available indicator. Since the low frequency tone is radiated only during idle periods, its absence during busy periods will prevent the operation of the indicator even though the radio station on the train has moved into the service zone of the terminal radio station. The radio station on the train is also provided with a noise detector circuit which pro' duces a control voltage to prevent the operation of the indicator when the signal-to-noise ratio is not satisfactory for communication purposes.- In addition, the radio terminal station is provided with another low frequency tone which is used to modulate the carrier only when the telephone at the station on the train has been left off its holder, thereby creating a busy condition. When the carrier modulated with this second low frequency tone is received at the train station, the tone is separated by filtering and is employed to discontinue the operation of the radio transmitter on the train after it has inadvertently been left in operation due to failure to vrestore the train telephone instrument to its holder.

These and other features of the invention are more fully discussed in connection with the following detailed description of the drawing, in which:

Fig. 1 is a pictorial representation of a radio telephone communication system having a plurality of terminal radio stations and a plurality of mobile radio stations;

Fig. 2 shows a telephone booth with an unattended coin box telephone and associated radio equipment located on a passenger railroad train;

Fig. 3 is a schematic representation of the telephone and radio equipment at a terminal radio telephone station;

Fig. 4 illustrates the radio equipment and its associated control equipment at the train radio station; and

Fig. 5 illustrates the telephone equipment and its associated control equipment at the train radio telephone station. l

In Fig. l, a radio telephone communication system is shown to include four radio telephone transmitting and receiving terminal stations TI`.-

T2, T3, and T4, together with a number of subscribers stations, some being located in automotive vehicles VI, V2, V3, V4, V5, and V6 and one being located in a railroad passenger train R. Each of these subscribers mobile stations VI to V6,. inclusi-ve, andR is equippedwith radio telephone transmitting and receiving equipment. Each of the terminal stations TI to T4, inclusive, is provided with both a transmitting an tenna AI, A3, A5, and A1, respectively, and also a, receiving antenna A2, A4, A5, and A8, respec-V tively. The subscribers mobilestationthat is located in the railroad train R; which is tliestaf tion with which this invention islparticularly concerned, is also provided with" a transmitting antenna A9 and a receiving antenna AID.

The radio terminal stationsTI to T.4,.inclu sive, employ the well-known line-of-sightmethod of radio transmission and reception. Thus, each one serves a particular geographic zone ZI, Z2, Z3, and- Z4, respectively. havinglimits 'determined by the heightsof the associatedantennas AI to A8, inclusive.- the amount of power radi.- ated-and the nature of the terrain. In this par-l ticular embodiment of. the invention, the railroad train- R travelsbetween New York, New York, and- Washington, D. C., and the terminal sta-v tions: Tl to T4, inclusive, are located in the principal cities along the route.A located-in Washington, D.- C1.; stationvTZ. is 1oca-ted in Baltimore, Maryland; station T13-is lof catedrin Philadelphia, Pennsylvania; andA sta1l tion-T4is-loca-ted in.-Newark;.N.ew Jersey. indicatedin'Figf.; '1, the serviceaoriesfZlA 'to Z4,in elusive, do not-overlap.` Thereforea, asthe -rail.

roadrtrainl',- trayelsg-alongfits, route, itwill leave oneservice zone: and enter ageographic'- areaf having'no radiortelephone facilities. Later, it

will leave the. noservice available areaand will` enterl adifferentV zone in; whichY radio telephone service is available. Still later, it will; leave. this; zone and will again travel for somey periodjoftime. through an area having nor radio telephone-service available. This procedure is. repeated until the'train R reaches itsnal destination.

As` the service zones and the no service," areas have no visible lines" of demarcation. it canA be. understood that itis desirable'that theradiog teler phone station on-the'train R betequippedwith readilyV discernible indicator: which wiilherzactu atedf only when the train R isfin; oneof the serv@- ice zones ZI Ito-Z4; inclusive. Since, in this-embodiment of the' invention, the radiov telephone; station on theV train R' is an unattendedV station having a coin box. telephone, there .isA no attendant on the train R; who could manually opA erate the indicator. Therefore, it is necessary` that the telephoneservicefavailable? indicator be'operated automatically whenever` the train 1% enters one of the service zones ZL to Z4, inclusive. the 'indicator be automatically discontinued whenever thetrain R leaves oneA of the service zones ZI to Z4; inclusive.

Theportion. of the frequencyl 4spectrum thatis assigned as a communication channel for'usebe tween the. radiostation onthe trainR and the terminal stations TI to T4, inclusiveis the same as that assigned for use between the-n iczl'oile-ve` hicular radiostations Vl.to V6, inclusive; andthe terminal stations` TI to T4^," inclusive. this common use of the communi'cation'l channel, when .oneof the automobile radio stations VI to V5,..inclusive, in oneof the seryice zone'sZl vtoZ4, inclusive. Aisusineth'e chanr1e .1,l a passengerA 0n- Thus,l station Tlvis It is also necessary that theoperation. ofl-` Due yto scribed hereinafter. the sign I appears to be blanlc.I but, when. the' the train R will not be able to use the radio telephone station on the train R if the train R is at that time in the busy zone. Accordingly, it is desirable that the telephone service available indicator at the radio station on the train R be automatically controlled so that it will .not be operated when'the communication channel is being used by another subscribers radio telephone station in the same zone as that in which the train R is located at a particular time. It is to be noted that, since the system employs the line-of-sight method ofA radio transmission and reception, use of. the commoncommunication channel in one service: zone will not prevent it from being availablior useindependently in another service zone at the same time.l

Since the radio telephone station on the train R' is unattended, as was stated above, there is no attendanton the train R who can observe transmission conditions to determine whether the instantaneous signal-to-noise ratio is satisfactoryv for commercial use of the communication'system by a passenger on the train R.. Consequently, it isadvisable that thetelephon`e service available indicator at the lradiostation on the train R be automatically controlled so that-it will not be operated when the instantaneous signal-to.noise tioneoll conditionsandrequirements is illustrated in Fig; 2, whereinitis show-nf in. the formofz'atranslucent sign Il mounted'in ahousing= 2. The, housing 2 contains a;so.urceo1 illumination, such as an electric lamp L, which. is. shown in Figi. 5

The electric current: f -o1",lighti-nf.s= the lamp Listurned off and on in accordance withthe above-- mentioned conditions by.- meansfthat are de- When .the lamp-L is not lit,

lamp L is lit, the words. telephone service available become clearly visible. The sign I, together-With the housing 2, is mounted in a con-- spicuous position outside a booth 3.

The booth 3 is situated at a convenient location on the train R, such asin the club car. 1 It is provided with a door 4 and, in addition to a chair 5 and the usual lamps 6, containsl a. telephone handset 1 adapted to be held. byfahookswitch 8: mounted on a coinzboic 9. Instructions forthcsubscribers use of. this. unattended, coin box, radio. telephone servi-.cet are prntedon, a card- IB attached to a wall of. the;booth 3'. The. booth'3v also contains a shelf; II positioned.convenientlyv A bell-.box |21: is-attached tothe bottom surfacaof; the shelf II in an inconspicuous'- position. Tlre'bellvbox-"IPA beneath the telephone. handset 1.'

contains a bell I3 and. two push-button typeof switches I4 and I5', these itemsbeing shown in;`

Fig. 5. Also attached to the bottonmsurface of the shelf I I is a junction box Isfroxn which three electric conductors I1, I8, and `le'xtend;V Con-v ductor I1 is connected to the housing' Z, conductor I8 is connectedto the bell box- IZ,"andfconductor I9'is connected'to-the coin box 9. These three conductors I1, I8, and I9 are cabled toigether inside the yjunction box- I6, and the resulting cable is passed through an openingin the associated wall of the booth 3 to an adjoining apparatus cabinet 20. The apparatuscabinet 20- contains a conventional radio t'ransmitter'2l anda conventional radio receiver' 22, both` of whichA are-indicated schexriaticallyi in Fig: 4: Also inside thev cabinet j E :is 'control equinientfslowi in nltgii-A 4 and 5, for controlling the-illumination of the"l signl." The cabinet 20 is provided with a'd'or 23 which is normally locked but-which may be unlocked'when it becomes necessary to-inspect, repair, or replace the enclosed equipment.

Fig. 3 represents schematically the arrangement of apparatus and equipment at any one of the terminal stations Tl to T4, inclusive, such as station T3. 3, a conventional telephone central ofiice 3| is connected by an electric cable 32-to the usual mobile service operators position equipment 33 whichincludes a normally open, manually operable, non-locking switch 34 and a.A normally closed switch 35 which isV automatically opened in a' mannerwell known to those skilled in the art whenever the operator initiatesl a call. The operators equipment 33 is connected by an electric cable 36 to the conventional radio control equipment 31 which includes a S600-cycle tone generator 38 and a 4100-cycle tone generator 39, both of which are of standard design. A conventional radio transmitter 4| having a transmitting antenna A5 is connected by an electric cable 42 to the controlV equipment 31; Similarly, a conventional radio receiver 43 having a receiving antenna A6 isconnected by an electric cable 44 to the control equipment 31. The radio receiver 43 is provided with'the usual codan relay 4'5 which is normally not energized but which, as

is well known tothose skilled in the art, becomes`v energized in response to the reception by the re-v ceiver 43 of carrier energy. By means of this arrangement of the'ed'uipment at the terminal station, a passenger on the railroad train R can call the mobile service operator and be connected to the telephone central oiiice 3| or to any of the mobileA vehicular 'radio stations within that particular zone. l A

The functions performed by the tone generators 38 adfie described hereinafter. It may be noted here, however, that in the idle condition with no'carrier energy being received by the antenna A6, the codan relay 45 is not operated, and a circuit is closed from ground 46, over the armature and backcontact of relay 45, through switch 35 which is now closed, through the 4100-cycle tone generator 39, and then over conductor 41 tothe radio transmitter 4|. Thus, in the idle condition, the 4l00cycle-tone is applied to the radio transmitter 4| where it is employed to modulate-*the carrier energy Which'is generated vin the transmitter 4| and radiated by the antennaV A5 to the radio station on the railroad train vR. This circuit is automatically opened to Vdisablethe generator 39`in response to I is open at both the normally open switch 34 and the front .cntact' of the codan relay 45. When carrieren'ergy radiated from any of the associated subscribers radio stations is received over the antenna A6, the" armature of the codan relay 45 is' operated to its front contact to connect "ground 46 to thel generator 38. Then, when the service operator manually closes the non-locking switch 34, a circuit is' closed fromgr'ound 46, over the Gf amature land-front contacto! the codan relay' 45,5 through the 3600-cycle tone generator switch 34, and then'over conductor 481to1tl1e1radiof transmitter 4|. Thus, the generator 38A is sub`` stituted for the generator 39 and the 3600-cycle tone is now employed by the radio transmitter 4| to modulate the carrier energy radiated to the radio station on the train R. For a reason explained hereinafter, the switch 34 is closely only momentarily so that the carrier radiated by the antenna A5 is modulated by the S600-cycle tonele. for only a brief interval of time.

Referring now to Figs. 4 and 5. which show thel equipment at the radio telephone station on the train R, it was stated above that, when the train R enters a service zone, such as the zone Z3, the receiving antenna AIU on the train R will re'- ceive the carrier energy that is radiated from the associated radio terminal station T3. It was also stated above that, in the idle condition, the carrier is modulated with a L1100-cycle tone. From the antenna All) on the train R, the tone modulated carrier energy received by the antenna AIU on the train R is delivered to the radio re-V ceiver 22, which is located in the apparatus cabinet 20, shown in Fig. 2, in the club car of the passenger railroad train R. In the radio receiver 22, the tone modulated carrier energy is demodulated in a well-known manner and is converted to audio frequencies. The audio frequency out put from the receiver 22 is supplied over a coni-' ductor 5| to the control grid of a thermionic amplifier 52. A portion of the plate output from amplier 52 is coupled over an obvious circuit to the control grid of'a combined ampliiler and" trigger tube 53.

In tube 53, the screen grid 54 functions asaplate for the control grid 50 and the cathode?T 53 and capacitors 56 and 51, is tuned tod-100g,

cycles. The other of these resonant circuits, consisting of coil 58 and capacitors 51 and 53, is tuned to approximately 2050 cycles. The voltages across these resonant circuits are separately rectied by rectiers 6| and 62, respectively. The rectiers 6| and 62 may be of any suitable type. such as germanium diodes, and are so arranged that theiroutputs are connected in series opposi-v tion to thejunction point 63". The net output of the rectifiers 6| and 62 is connected over an obvious circuit from the junction point 63 to the suppressor grid 64 of tube 53.' The voltage thus applied to the suppressor grid 64 functions asa control trigger voltage vfor the' purpose of controlling the conductivity of the cathode-anode circuit of the tube 53. l Y

For example, if the output of tube 52 Yconsi-sts' chiey of the 4100cycle tone, the output from rectifier 6| will predominate and a'positive voltage will be applied to the suppressor grid 64 with theresult that the cathode-anode circuit of the tube 53 will be rendered conductive. On the other hand, during busy periods when speech energy centering around 2050' cycles may be applied to the tube 52, the output ofthe tube 52,` in addition to containing energy of 2050 cycles, may also containA harmonic energy centering around 4100 y cycles. When energy centering around these two frequencies is applied to the tube 53, thescreen grid 54 will deliver this energy to the above-'mentioned resonant circuits-with the'result that therectier 62 will rectify the speech energy of 2050 cycles and rectier 6| will rectify the harmonic energy of 4l00`cycles". Since rectiflers lare 1connected. inseries opposition, thefnetvoltagetapplied from the junction peint 63 to v.the.-Slrlpiissorv grid 64- will-either bev negative or zero orat vleast not suciently positive to render the cathode-anode circuit of tube 53 conductive. This insures that the cathode-anode circuit of the tube 53 will be rendered conductive only in response to the reception of the 4100- cycle tone.

'As .was stated-above, since there is-no attendantonA the train R who can measure the instantaneous signal-to-noise-ratio, it is necessary that this `beperformed automatically so that the sign I, sho-wn in Fig. 2, `will not be illuminated when .the .instantaneous signal-to-noise ratio is not satisfactory for commercial use of the system. Accordingly, a portion of the plate output from amplier 52 is coupled over an obvious circuit to a lter5|l having a low-pass characteristic essentially at from 200 to 2000 cycles. The output of the-lter-Bll isV connected to the control grid of an amplifier having its plate supply derived over a-circuit extending through the resistors 83 and 84, along a conductor 85, over the middle bottom armature and-contact of4 non-operated relay 16, and then to battery86.

The amplied noise currents are rectified by a rectier 81, which may be of any suitableA type such as a germanium diode, to produce a voltage that is negative with respect to ground. This negativer-voltage is` applied over a conductor 88 to the junction point 63 where it is combined with the netpositive voltage produced bythe rectication of'thellOO-cycle tone. If the resulting voltage thus applied to the suppressor grid 64 is negative with respect tovvground or is less-than approximately three volts positive with respect .to ground, the cathode-anode circuit of tube 53 will 4either be non-conductive or not sufciently Iconductive to accomplish any further circuit operations. However, if the resulting voltage is aproximately three or more volts positive with 'respect to ground, the cathode-anode circuit of tube 53 will become suiliciently conductive to complete a. path extending from ground 89, through thecathode-plate circuit of tube 53, outover conductor B5, through the Winding of relay 1|, and thenv to battery 80. The closing of this -path serves to energize the relay 1| which thereupon operates its armature to its front contact to'completean obviousy circuit for energizing relay 12 and causing it to operate its. armatures.Y Itis to be noted that the-pass-band of the lterh is selected to be within the speech frequency range in order thatthis portion of the frequency spectrum may be automatically examined in order to prevent the initiation of the transmission of speech energy when unfavorable noise conditions exist.

The operation of the top armature of relay 12 completes a circuit for energizing relay 13, this circuit extending from battery 14, top armature and make contact of relay 12, over conductorv 15 to relay 13, through the Winding of relay 13. and then over the top unoperated armature and contact of relay 16 to ground 11. When relay 13 thus becomes energized, it operates its armatures. The operation of the bottom armature of relay 13 closes a circuit for current from battery 18 to ow along conductor 19 to energize relay 8| Upon being energized, relay 8| operates its armature to close a circuit for current to ilow from a source of power supply, such as the battery82, through the lamp L thereby lighting the lamp L.

.Since` vthe lamp L, as was Ystated above,is located. inf .the housinaLshownin lichtfins of the lampLwilLcause .the wards telephone service available" on .the f sign l, also shown. in Fig. 2, to become clearly visible. This serves to indicate to passengers on vthe railroad train R that the train has entered a service zone having radio telephone facilities, that the assigned communication channel is idle, and that the instantaneous signal-.to-noise ratio is satisfactory for commercial use of the assigned communication channel.

It the magnitude of the noise energy should in.- crease tosuchan extentas tolcause the recter 81 to produce a negative voltagethat is suciently large-to cause the cathode-anode circuit of the tube 53 to become non-conductive, then relay 1| will release its ,armature thereby causingv `the release of thearmatures ofv relay 12 which, in turn, effects the releaseof the armatures of relay. 13. The release ofthe armatureof relay 13 causes relay.8| to release itsarmature thereby extinguishing the lamp L and causingthe sign I to appear to be blank, .as .was mentioned. above, thus in-4 dicating that .the system is not incondition for use bya passenger on the train.

In order to preventthe lamp L from ickering oi and onv due .to borderline conditions, once the lamp L has been lit the noise amplifier 10 isdegradeda small amount. This is effected when relay 13 first becomes energized and operates its top armature .to connect resistor in parallel with resistor83 thereby reducingthe. gain of the noise amplier .'land allowing ythe circuit signal.- to-noise ratio to. degrade by a predetermined number ordecibels before the cathode-anodecircuit of tube53 is'rendered non-conductive. This produces a hysteresisy effect .in the determination of the signalew-noise operateandreleasepoints thereby improving the stability of theoperation of the sign I.

Assuming. ,that` the lamp L is litandthata passenger .wishes to make a call, he-enters. the booth 3,.shown in llig. 2, and removes the. telephone handset 1 from its hook switch 8 thereby I closing the hook switch contacts. Closure of the top hook switch contact completes a. circuit from ground-92. over vconductor 93, through thewinding of relay 94, and then .to battery 95. This energizes-relay-94 which operates its. armature to completea circuit extending from ground 96, over the inner top .armature andcontactfoif non-operated relay 91, along conductor ...98, through the :winding of relay 16, and then over the operated inner top Aarmature and contacto! relay.12.to..battery 99. Relay 16-nowbecomes energizedand operatesl its armatures, ythe inner bottom armatureclosing a lockingdip path-to battery |0|. Operation of thev next tothe top armature opensthesenergizing circuitof relay 13 andcauses it,.in turnfto open thgialng circuit of relay 8| :thereby extinguishing the lamp L. Operation of the outer top amature connects capacitor |02 in parallel withcapacitor 56 thereby changing the resonant frequency` of the associated 4tuned circuit-from 4100 cycles-'to 3600cycles forfa purpose-explained hereinafter. Operationv ofl the middle -bottom armature disconnects-battery 86 vfrom the plate of the noise amplifier 10. Operation of thel next to the lowest top armature applies ground 11 over conductor |03 to'control equipment in the radio transmitter 2| for conditioning :it for operation. At the Sametime, a -circuitds yclosed from ground 9B. over -the-annature-and contact of relay- 94a1ong ,conductora-through .the .winding .ci ,relay I 04.

thenralong.1conductor-,|0.5, and over the inner operated-amlature of relay 12-to battery 89. Relay |04 consequently becomes energized and operates itsV top armature to apply ground |06 over conductor |01 to a control circuit in the radio transmitter 2| for the purpose of starting its dynamotor. The transmitter 2| is thus placed in operation and radiates its assigned carrier energyigut over the transmitting antenna A9. At the saine time, the energization of relay |04 completes a circuit extending from the receiver of the telephone handset 1 along conductor |2|, over the normally closed contacts of the monitoring switch I5, along conductor |22, over the released bottom armature of relay 91, along conductor |25, over the bottom operated armature of relay |04, down along conductor |26, and then over conductor |21 to the conventional audio output circuits in the radio receiver 22.

The calling passenger now gives the mobile service operator at the associated terminal radio station the number of the party he is calling. The service operator, in turn, informs the calling passenger of the-amount charged for the call. The passenger then deposits the required coins in the coin box 9, shown in Fig. 2, where they actuate the coin transmitters |08 which are connected over the operated bottom hook switch contacts and along conductor |09-to the radiotransmitter'Zl. The service operator then completes the connection and the passenger proconductor |03 leadingv to control equipment in the radio transmitter 2|. The release of the 'top armatureof relay |04 removes ground |06 from conductor |01 leading to the dynamotor control circuit in the radio transmitter 2|. The

removal of grounds 11 and |06 from conductors |03 and |01 'stops the dynamotor in the radio transmitter 2|, effects ythe termination of the `transmission of carrier energy, 'and restores the radio transmitter 2| to 'its-idle, condition.

In theevent that the passenger should attempt to make a call -when the lampy L is not lit,vre moval of the handset 1 from Vthe hook switch 8 would effect the operation of the armature of relay 94 in the manner described above. However, since relays 1| and 12 are not energized at this time; a path is nowclosed from ground 96, through the winding of. relay 91, along conductor normally closed contacts of the emergency switch |4, along conductor. |12, over cony,

'ductor' ||3, released outer bottom armature of relay 16,- along'conductor I I4, and then over the released' top armature of relay12 to battery 14.

' This 'serves to energize relay 91 which operates its armatures and connects the receiver of the "handset 1 along conductor |2|, over the rior'- mallyr closed contacts of the monitoring switch I5, 4along conductor |22, over the operated-bot'- tom armature of relay 91, and then along con- ,ductor |23 to thebuzzer |24.. Thus thereceiver 1v is disconnected from the circuit leading to the audio'output of the radio receiver 22 and the vpassenger is prevented from listening to a call that mightbeinprogress between other stations.

'tom armature offrelay 16 to battery |0I such as the vehicular stations Vl toVS.- inclusive, shown in Fig. -1. l Y

The operation of the outer top armatureof relay 91 connects ground |3| over conductor |32, along the armature of relay |33, and then through the winding of relay |34 to battery |35. This causes relay |34 to operate its armature which causes relay |36 to become energized over an obvious circuit. Relay |36 now operates its armature which closes a circuit for energizing relay |31 which, in turn, closes a circuit for energizing relay |33. When relay |33 now operates its armature, it opens the energizing circuit of relay |34. Rel-ay |34 is of the slow-torelease type and does not release its armature for milliseconds. Relay |36, which is also of the slow-to-release type, now releases its armature after a l25-millisecond delay. This causes the buzzer |24 to operate until relays |31 and |33 have released and relays |34 and |36 have operated. The operate time and the release time of the buzzer |24 are equal sincetliese times depend on the release time of relays |33 and |31 and the operate time of relays |34 and |36vin one instance and on the operate time-of relays |33 and |31 and the release time ofrelays |34 and |36 in the other instance. Thus. when the buzzer |24 is operating, a toneI at the buzzer frequency will be heard in the receiver of the handset 1. 1.;,f

When the service operator at the 'terminal station wishes to call theA mobile stationkomthe train, the conventional selective calling signal is transmitted from the terminal station: This signal is received 'at the radio receiver 22- and operates the usual selector which applies elec,- tric current over conductor |38 to the ringer l|39 located in the bell. box |2 shown -in AFigJZ.

The ringer |39 functions in the usual manner'to ring the bell I3. At the time that thegsgnvice operator initiates the call, the switchi35 shown in Fig. 3 is automatically opened, as was described above, thereby discontinuing the transmission of the 4l00cycle idle tone which, in turn, causes relay 1| to release its armatures. Since this tends to prevent the radio transmitter 2| from being placed in operation'when the call is answered by the removal of the handset 1 from the hook switch 8, a portion of the current from conductor |38 is supplied over conductor 4| to the make-before-break contacts associated with the bottom armature of relay |42. This current passes through the winding of relay |42 and then over the released armature of relay 1| vto ground |43 thereby energizing relay l42. Relay |42 now operates its armatures and locks up over a path from ground |43, released armature of relay 1|, winding of relay |42l bottom armature of relay |42, along conductor |44, and then over the released inner bot- The operation of thetop armature of relay |42 closes an obvious circuit` from ground |45 over conductor |46 to energize relay 12. :The resulting operation of the armatures of relay 12 places the system in the condition described above for starting the radio transmitterv 2| in response to the removal of the handset 1 from the hook switch 8. Y y

There may be occasions when a passenger, after making a call, forgets to replace the tele'- phone handset 1, on the hook switch 8 and. instead, inadvertently leaves it resting on the shelf shown in 2. This is a serious departure from the proper operating procedure because, as

was'desibed above', the' circuit' is designed'to cause the carrier to be radiated fromI the radio transmitter 2| when the handsetA 1 is oiiithe hook switch 8'. With the'carrier thus being radiated from the transmitting antenna A9, it will be received by the receiving antenna A6 at the terminal station and will actuate the radio receiver 43 to cause a calling indicator to be operated in a Well-'known manner at the service operators position. When the occurrence of this condition is recognized by the service operator answering the' call indicator without obtaining any response, the'service operator operates the non-locking key 34momentarily to complete the circuit for applying the S600-cycle tone generator to the radio transmitter 4| as was described above.

The carrier modulated with the S600-cycle tone is received at the radio receiver 22 on the train Where it is demodulated and applied over conductor 5| to the tone ampliiier 52; which in turn, applies it to the control grid ofthe tube 53. Since relay 16 is now operated, due to the handset 1 being oli the hook switch 8, condenser |02 is'connected in parallel with condenser 56, as was describedabove, with the result that the associated resonant circuit including coil 55 is now tuned to 3600 cycles. Consequently, the rectier 6| will now apply a positive voltage to the suppressor grid 64 thereby rendering the anodecathode circuit of tube 53 conductive. It'should be noted that, since relay 16 is now operated, battery 86- is disconnected from conductor 85 leading to the noise amplifier 10 which is consequentlyv disabledwith the resultthat noI oppos ing Voltage from the rectifier 81 will be applied over conductor 88 to the junction point 63 at this time. When the anode-cathode circuit of tube =53 is now rendered conductive, it effects the energization of relay 1| which operates its armature. This causesrelay 12 to operates its armatures in the manner described above. Prior to this energization of relay 12, the operation of relay 16 had closed a circuit extending from ground 11, over the operated inner top armature of relay 16, along conductor |5|, through the Winding of relay |52, and then over the released top armature of relay 12 to battery 14. This had energized relay |52 which had operated its armatures and had locked up over a path extending from battery |53, top operated armature of relay |52, winding of relay |52, conductor |5|, and then over the operated inner top armature of relay 16 to ground 11.

Consequently. when relay 12 now becomes'energized, it closes a circuit extending from battery` 14, over the operated top armature of relay 12. over the-operated bottom armature of relay |52, then along conductor I|2, over the normally closed contacts of the emergency switch |=4, along conductor III, through the winding of relay`91, and then over the operated armature o1 relay 94 to ground 96. This eiects the'energization of relay 91 and causes it to operate itsarmatures. The operation of the inner top armature of relay 91 opens the previously described energizing circuit of relays 16 and |04 which there'- upon release their armatures. 'I'he release of the next-to the lower top armature of relay 16 disconnects ground 11 from conductor |03 thereby discontinuing the operation of the radio transmitter 2| and stopping the radiation of its -carrier energy. At the same time, the operation of the bottom armature of relay 91 disconnects the telephone receiver in the telephone instrument 1 from the conductor |21A leading tothe audio outputl circuit of the radio receiver and 12 connects the-:telephone receiver-'1n instrument `1 to the outputcircuitoffthe |24'. Thel operation ofthe outer top armature of relay 91 starts the operationof the'buzz'er |24 in the manner described above.

Since no carrier energy is now being radiated l by the antenna A9, the codan relay 45v atthe terminal station releases its armature to close the circuit for applying the t100-cycle tone tothe transmitter 4|. 'I'heresulting tone modulated carrier will be received b'y the radio receiver 22' and will again eiect the lighting of the lamp L in the manner previously described. If a' passenger on the train sees the telephone service' available sign I illuminated and enters the booth 3, he will iind the telephone linstrument 1 resti ing on the shelf Upon picking it up, he will hear the busy tone'v produced by the buzzer |24. In accordance with the instructions printed'onv the card 0 shown in Fig. 2, the passenger replaces the telephone handset 1 on the hook switch 9 thereby opening the Vhook switch contacts. The opening of the upper set of hook switch contacts opens the energizing circuit of relay 94- which releases its armature thereby opening the energizing circuit of relay 91 and causes it to release its armatures. When relay- 91 now releases its armatures, it discontinues the operation of the buzzer |24, disconnects the"telephonereceive1v`4 inthe telephone instrument- 1 from-the output cirv cuit of the buzzer |24-, and restores 'the remairid of the station equipment to itsv normal idle con# dition. The passenger then removes' the telephone handset 1 from the hook switch 8 and "pro-v ceeds to make his call in the normal mamier'dea scribed above'.

If an emergency arises; and the'conductor on' the train Wishes to make'a call but, uporilitting the telephone handset 1 hearsa busy tone; he momentarily operates' the emergency push 'button I4. This opens the normally closed lower'set of push button contacts which, in turn opens the energizing circuit of 'relay 91 thereby discontinu-` ing the operation of the buzzerv |24. At' the saine` time, the normally open upper set of push button contacts becomes closed thereby closing' a' circuit extending from' battery |51 through thev now closed upper set of push button contacts ofs'witeli I4, along conductors |58 and |05`,,throu`gh"th'e windin'gsof relays |04 and 16 in parallelgalorig conductor 98, over released inner top' arniature of relay 91, and then over the operated armature of relay 94 to ground 96. This energizes relays |04 'and 16' which operate their armaturesand lookup from battery |0|, overv the inner"bottoniv armature of relay 16, through the-winding--ofref lay 16, and'then along conductor 98"`vto'ground 96: This starts the transmitter 2|'in the manl ner described above-so that-the train'conductor can now proceed with his call.

Periodically, a telephonemaintenance man will board theftrain to inspect the radio! telephone equipment and tov makefany. repairs or adjustments-that may be necessary; There may; be'l oc-A casions when these inspections will be madewhen' the train is in a storage-yard at night and-no idle tone is being transmitted from the associatedterminal radio station and,- consequently, relay 1,6 will not be-energized. Underthis condition, when the maintenance manlifts .the .telephone handset 1 off the hook switch 8, relays- 94' and`91' will become energized over the circuits` described above to operate the buzzer |24 and to connect the telephone handset to" .the output circuit; of' the m. Uponv4 hearingt tms busy" tciiie. thisr maintenance' man momentarily operates the monitoring push button switch I to close its normally open upper set of contacts thereby connecting the telephone receiver in the telephone instrument 1 over conductors |2| and |59 to conductor |21 leading to the audio output circuit of the radio receiver 22. If the maintenance man determines by listening that the communication channel is busy, he waits until it is idle. When it becomes idle, he momentarily operates the emergency push button switch I4 which places the radio transmitter 2| in operation in the manner described above. Carrier energy is now radiated from the antenna A9 and the maintenance man proceeds with his call.

It is to be understood that the invention has been shown and described with reference to a specific embodiment for the purpose of explaining the principles and features of operation and that various modifications may be made without departing from the scope of the invention which is to be limited only by the claims appended hereto.

What is claimed is:

l. A passenger vehicle radio telephone station comprising a radio transmitter and a radio receiver carried by a passenger vehicle for the transmission and reception of intelligence signals, a telephone instrument connectible to said transmitter and said receiver, holding means for holding said instrument during idle periods, a booth carried by the vehicle for enclosing said telephone instrument, an indicating sign affixed to said booth, a lamp for illuminating said sign, a lighting circuit for lighting the lamp, frequency selective means for effecting the closing of said lighting circuit, said frequency selective means being actuated by the reception by the radio receiver of electric energy of a preassigned frequency during idle periods when no intelligence signals are being received by said receiver, noise responsive means for effecting the opening of said lighting circuit, said noise responsive means being actuated by the reception by the radio receiver of noise energy having a magnitude exceeding a preassigned critical value, and electroresponsive means actuated by the removal of said instrument from said holding means for opening said lighting circuit.

2. A passenger vehicle radio telephone station in accordance with claim 1 in which said frequency selective means comprise a resonant circuit, a first rectifying device coupled to the output of said resonant circuit, a second rectifying device coupled to the output of said noise responsive means, rst circuit means for coupling the outputs of said rectifying devices in series opposition to produce a resultant voltage, a thermionic tube having a plurality of electrodes. and second circuit means for applying said resultant voltage to one of said electrodes.

3. A passenger'vehicle radio telephone station in accordance with claim 2 and having third circuit means for coupling a second one of said electrodes to the input of said resonant circuit.

4. A passenger vehicle radio telephone station in accordance with claim 3 and having fourth circuit means for coupling the output of said radio receiver to a third one of said electrodes for controlling the conductivity of the space path between a fourth one of said electrodes and the second one of said electrodes, the conductivity of the space path between said fourth electrode and a fth one of said electrodes being controlled by said mst-mentioned electrode. A'

5. A passenger vehicle radio telephone station in accordance with claim 2 in which saidfrequency selective means comprise a second-resonant circuit, a third rectifying device coupled to the output of said second resonant circuit, and coupling means for coupling the output of said third rectifying device and the output of said first-mentioned rectifying device in series opposition.

6. A passenger vehicle radio telephone station in accordance with claim 5 in which said firstmentioned resonant circuit is tuned to a frequency in the higher portion of the speech frequency spectrum, said second resonant circuit being tuned to a frequency in the intermediate portion of the frequency spectrum, and said noise responsive means including a low-pass nlter having its pass-band located in the lower portion of the frequency spectrum.

7. A radio telephone station comprising in combination a radio transmitter adapted to radiate carrier energy, a radio receiver adapted to receive carrier energy, a telephone instrument connectible to said transmitter and said receiver lfor the transmission and reception of intelligence signals, holding means for holding said instrument during idle periods, an electroresponsive indicator associated with said telephone instrument, an energizing circuit for actuating said indicator, frequency selective means for effecting the closing of said energizing circuit,said fre.- quency selective means being actuated by the reception by the radio receiver of electric energy of a preassigned frequency during idle periods when no intelligence signals are being received by said receiver, noise responsive means for effecting the opening of said energizing circuit, said noise responsive means being actuated by the reception by the radio receiver of noise energy having a magnitude exceeding a preassigned critical value, and rst electroresponsive means actuated by the removal of said instrument from said holding means for conditioning said radio transmitter for operation and for opening said energizing circuit. i

8. A radio telephone station in accordance with claim 'T in which said preassigned frequencylies within the higher portion of the speech frequency spectrum, said noise responsive means including a low-pass lter having a fiat characteristic and having its pass-band located in the lower -portion of the speech frequency spectrum.

9. A radio telephone station in accordance with claim 7 and having second electroresponsive means for reducing said preassigned critical value substantially simultaneously with the closureof said energizing circuit. y

10. A radio telephone station in accordance with claim 7 in which said frequency selective means include two resonant circuits, one tuned to a, fundamental frequency and the 'other tuned to a harmonic of. said fundamental frequency, a first rectifier for rectifying the output-of one of said resonant circuits, a second rectifier for rectifying the output of the other of said resonant circuits, means for connecting the outputs from said rectiers in series opposition to produce a resultant voltage, a thermionic tube having a suppressor grid and a screen grid, first circuit means for coupling said screen grid to the inputs of said resonant circuits, and second, circuit means for applying said resultant voltage` to said suppressor grid.

11. A radio telephone station in accordancev with claim 10 and having tuning means cm1...

asomar! trailed-'1 by-said-rst' electroresponsivei-rneans for tuning one-or 'said-resonant circuits to adlfferent frequency.

12. AJ radio telephonestation in' accordance with claim 10 in vvvhich said noise responsive means includes a lter, an amplii'ier'coupled te the output of the lter, a third rectifier coupled to the output of the ampliiier for rectifying its output energy, and third circuit means for-combining the output from said third rectifier with said resultant voltage for application to said suppressor grid'.

13. A` radio telephonestation in accordance' with claim 12and having fourth circuit meanscontrolled bysaid second electroresponsive means for degrading said-amplifier by a preassigned amount.

14.. In a radio telephone communication system for providing radio telephone communication service for passengers onl a vehicle traveling through a number of geographic zones; some having radio telephone service facilities and others having no Yradio` teleplfioneservice facilities, aradio telephone station on saidY vehicle', said station comprising a telephone instrument and-holding means for holding saidinstrument during idle periods, indicating means forY irrforming the passengers that the vehicle is travelingthrougha radio telephone service zone, saidindicatingmeans comprising anindicator car,- riedby-the'vehicle, a source of electric energy; anl energizing circuit for connecting 'said source to the indicator for actuating said indicator, rstelectroresponsive means for effecting the opening and-closing of said energizing'circuit.

a frequency-'responsive circuit responsive to electrie-energyof apreassigned frequency for eiTectingthe control of the operation of said firstl electroresponsive means, radiating meansin each-v of '-said radio telephone service zones for radiatingcarrier energy' modulated only with electric energyl ofsaid preassigned frequency, receiving means on the vehicle for receiving the modulated' carrier energy thatis radiated in the zone through which the vehicle is traveling, demodulatingl means for demodulating said received modulated carrier energy, circuit means for applying demodulated energy of' said preassigned frequency to said'- frequency responsive circuit, andi second' electroresponsive means actuated bythe removal of. said instrument from. said holding meansf for effecting-the opening of vsaid energizing. circuit.

15. Ina radio telephone communication system in accordance with claim 14- andhaving third' electroresponsive' means for discontinuing in the zone through which the vehicleisstravelingf the modulation of said carrier energy with. electrie. energy of said preassigned frequency, said thirdfelectroresponsive\means being actuated-"byV the removal of the'k telephone instrument from said; holding means.

16. In a radiov telephone communication-sys-- tem in: accordance` with claim-14' in which said radio telephone station includes a radio transmitter adapted` to radiate carrierenergy. andV starting means for eiecting the radiation of carrier energy by said transmitter, said starting means being actuated by the removal oi" said telephone instrument from said holding means, said. radio telephone service facilities: includingl receiving means for receiving said carrier energy radiated by said transmitter and also inciudi'ngv an electroresponsive instrumentality for discontinuing within the service:- zone-in which' 752 16 the vehicle is traveling-the modulation-0MM ner-energy with Ielectric energyi of "said l preas signed frequency, said electroresponsives instru-1 mentalitybeing actuated by the reception by saidl receiving means of carrier energy radiatedby said radio transmitter.

17. In a radio telephone communication system comprising in combination a terminal radio station and a su-bscribers radio station, said sub scribers-,station including a radio receiver, a telephone instrument, a holder for holdingY said instrument during idleperiods, a radio transmitter, a control circuit for effecting the. energization of said transmitter, an instrumentality` for opening said control circuit for eiecting the deenergiza-tion of saidY transmitter, saidinstrumentalityV beingactuated in response to the holding of' said` telephone instrument bysaid holder, said system beingcharacterized'by having-control means forlactuating said instrumentality during periods when the'telephone instrumen-t is removed from said holder, saidcontrol means comprising radiating means at said' terminal station for radiating carrier energyy modulatedewith electric energy of a preassigned frequeney, and electroresponsive means at said subscribers station, said electroresponsive means being actuated bythe reception of said-modulated carrier energy by said radio receiver-for eiect y ing the actuation-of said-instrumentality.

18. Ina radiotelephone communication system in accordance with claim-171 and-.having an electroresponsive alarm device atsaid subscrib. erfs station, said alarm device'having an output circuit, and; additional electroresponsive.v means. at said subscribers station for initiating the op.-. eration of said alarm-device and forv electricallyconnectingsaid telephone` instrument to said4 alarmv output circuit, said additional electroresponsive means being actuated by the reception. of saidV modulated carrier energy by Saidradio` receiver during periods when said telephone in-. strument is lremoved from said holder.

19; In a radio telephone communication sys-. tem in accordance-with claim 17 and having. ade, ditional electroresponsive means. at saidlsubscrilai-- ers station for closing said controlcircuit for.v effecting the energization of. said radio transmitter, said radio transmitter being adaptedto. radiatecarrier energy upon being. energized, receivingA meansat said terminal station torres. ceivingthe carrier energy radiatedbysaid radin.l transmitter, a control electroresponsivedevice at said terminal station for discontinuing .thernodih lation of carrier energy at said. terminal station with electric energy ofL said preassigned fren. quency, said control electroresponsive device liel ing actuated-by the reception by: saidreceiving meansof carrier energy radiated by said.radio. transmitten` 20.y A radio telephone .communicationy system: in accordancewithiclaim v1'7v and having. aA circuit for modulating the carrier energy radiatedirom said'- terminal station with electric energy; of;A av second preassigned. frequency different fromsaid first mentioned preassigned frequency; said. circuit being opened by the. actuation of saidieiel troresponsive means, and an additional instrumentality foralternatively opening .saidcircuit'l for discontinuing the modulation off.v said carrier: energy with electric energy of said' seeondpre-c assigned' frequency.

21. A radio telephone communicationzsystemf in accordance with claim 20. in' Whichzsaidlirst` mentioned preassigned frequency and saidzseconet.

preassigned frequency are both within the speech frequency spectrum.

22. A radio telephone communication system comprising in combination a terminal radio station and a subscribers radio station, said subscribers station including a radio receiver, a telephone instrument, holding means for holding said instrument during idle periods, a radio transmitter adapted to radiate carrier waves when energized, control circuit means for controlling the energization of said transmitter, first electroresponsive means actuated by the removal of said instrument from said holding means for closing said control circuit means for effecting the energization of said transmitter, radiating means at said terminal station for radiating carrier Waves, first modulating means at said terminal station for modulating the carrier waves radiated therefrom with electric energy of a rst assigned frequency, second electroresponsive means at said subscribers station actuated by the reception of said modulated carrier waves by said receiver during periods when the telephone instrument is removed from said holding means for opening said control circuit means for effecting the deenergization of said transmitter, and second modulating means at said terminal station actuated by the deenergization of said transmitter for modulating the carrier waves radiated from the terminal station with electric energy of a second assigned frequency.

23. A radio telephone communication system comprising in combination a terminal radio station and a subscribers radio station, said subscribers station including a radio receiver, a telephone instrument, holding means for holding said instrument during idle periods, a radio transmitter adapted to radiate carrier Waves when energized, control circuit means for controlling the energization of said transmitter, first electroresponsive means actuated by the removal of said instrument from said holding means for closing said control circuit means for effecting the energization of said transmitter, radiating means at said station for radiating carrier'waves, first modulating means at said terminal station for modulating the carrier waves radiated therefrom with electric energy of a first assigned frequency, second electroresponsive means at said subscribers station actuated by the reception of said modulated carrier waves by said receiver during periods when the telephone instrument is removed from said holding means for opening said control circuit means for eifecting the deenergization of said transmitter, an electroresponsive alarm device at said subscriber-s station, said alarm device having an output circuit, third electroresponsive means at said subscribers station actuated by the reception of said modulated carrier waves by said receiver during periods when the telephone instrument is removed from said holding means for initiating the operation of said alarm device and for electrically coupling said telephone instrument to said alarm output circuit, and fourth electroresponsive means actuated by the holding of said telephone instrument by said holding means for discontinuing the operation of said alarm device.

FRANK E. GISSLER. JOHN F. LAIDIG.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,949,136 Adair Feb. 27, 1934 2,007,399 Koch July 9, 1935 2,379,799 Haigis July 3, 1945 2,392,672 Koch Jan. 8, 1946 2,393,291 Clark Jan. 22, 1946 2,459,105 Halstead Jan. 11, 1949 2,479,305 Brown Aug. 16, 1949 2,501,091 Preston et al Mar. 21, 1950 2,501,986 Brockman Mar. 28, 1950 2,523,914 Molnar Sept. 26, 1950 

